The present invention is addressed to a process for assuring smooth and expected torque transitions for an automobile whose engine is stopped during traffic idling in order to reduce fuel consumption.
One of the primary goals of the automotive industry is to reduce fuel consumption and one of the methods being employed is stopping the engine during a typical traffic idling event. Such systems are currently in use in hybrid vehicles. In order to emulate conditions to which consumers have become accustomed with automobiles whose engines remain running during idling, it is necessary to take into account the xe2x80x9cfeel,xe2x80x9d responsiveness and smoothness of the start-stop operation of the engine during traffic stops.
Prior art addressed to automatic engine start and stop systems include systems which address undesired torque shock upon restart in a mode or in the motor driven in accordance with a target speed while holding the transmission in an unchanged state as disclosed in U.S. Pat. No. 6,275,759 B1. Other attempts at improved hybrid vehicle operation having automatic engine stop systems include U.S. Pat. No. 6,390,947 B1 which provides a hydraulic circuit for controlling oil pressure supplied to the automatic transmission so that the speed of the rise of the oil pressure can be increased when the engine is restarted in order to decrease the response time for starting the vehicle.
The present invention provides an interactive process involving communication and control between the transmission and the engine in order to overcome any smoothness problems occurring during engine shut-off and also to provide the expected torque response on re-starting the engine subsequent to a shut-off.
According to present invention, an engine is not shut down until the vehicle has stopped. The engine is restarted if the braking action is relaxed. Additionally, transmission elements are clamped during engine shut-down to minimize any transient torque disturbances. Furthermore, the present interactive process maintains application of the first gear friction elements during the stop period with a minimum possible energy from an auxiliary pump so that the transmission is ready to transmit torque immediately on restart. Furthermore, a limited amount of torque on restart is applied in a controlled manner to avoid any surge.
The present invention is. addressed to an automotive system which employs a modified alternator which functions to not only maintain the charge of the battery but also to start the engine after a traffic idle stop. Additionally, the present invention contemplates the use of an auxiliary transmission pump which is in addition to the normal transmission pump. This auxiliary electric pump functions to maintain transmission oil pressure when the engine is stopped for short periods of time as in the idle stop-start mode. Additional interactive process requires communication between the transmission controller and the engine controller.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.